Method of manufacturing semiconductor device

ABSTRACT

The manufacturing method of the invention performs over-etching to remove an upper portion of a conductive layer in a logic circuit area of a semiconductor device, simultaneously with etching out a stopper layer. The method subsequently patterns the conductive layer to form gate electrodes in the logic circuit area. The height of the gate electrodes is lowered, because of the removed upper portion of the conductive layer. In a subsequent process of polishing an insulating layer, even when the polishing rate of the insulating layer is not constant but varied and the insulating layer in the logic circuit area is polished relatively faster than the insulating layer in a memory area, this arrangement of the invention effectively prevents exposure of the gate electrodes in the logic circuit area, prior to exposure of stopper layers in the memory area.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method of manufacturing a semiconductor device including a memory area and a logic circuit area. More specifically the invention pertains to a method of manufacturing a semiconductor device, on which each of non-volatile memory devices formed in the memory area has two charge accumulation regions relative to one word gate.

[0003] 2. Description of the Related Art

[0004] One type of non-volatile semiconductor memory devices is MONOS (Metal Oxide Nitride Oxide Semiconductor) or SONOS (Silicon Oxide Nitride Oxide Silicon), in which a gate insulating layer between a channel area and a control gate is a multi-layered body of a silicon oxide layer and a silicon nitride layer and charges are trapped by the nitride silicon layer.

[0005]FIG. 22 shows a known MONOS non-volatile semiconductor memory device (refer to: Y. Hayashi, et al., 2000 Symposium on VLSI Technology Digest of Technical Papers p.122-123).

[0006] Each MONOS memory cell 100 has a word gate 14, which is formed on a semiconductor substrate 10 via a first gate insulating layer 12. A first control gate 20 and a second control gate 30 are formed as side walls on both sides of the word gate 14. A second gate insulating layer 22 is present between the bottom of the first control gate 20 and the semiconductor substrate 10. An insulating layer 24 is present between the side face of the first control gate 20 and the word gate 14. Similarly the second gate insulating layer 22 is present between the bottom of the second control gate 30 and the semiconductor substrate 10. The insulating layer 24 is present between the side wall of the second control gate 30 and the word gate 14. Impurity layers 16 and 18, each of which constitutes either a source area or a drain area, are formed in the semiconductor substrate 10 to be located between the control gate 20 and the control gate 30 of adjoining memory cells.

[0007] Each memory cell 100 accordingly has two MONOS memory elements on the side faces of the word gate 14. These two MONOS memory elements are controlled independently. Namely each memory cell 100 is capable of storing 2-bit information.

[0008] A memory area including such MONOS memory cells and a logic circuit area including peripheral circuits of memories are formed on an identical semiconductor substrate in a semiconductor device. A prior art method of manufacturing such a semiconductor device first forms memory cells in the memory area and subsequently forms peripheral circuits in the logic circuit area. The manufacturing method forms diverse wiring layers via an insulating layer, after formation of the memory area and the logic circuit area.

[0009] The manufacturing method forms an insulating layer of, for example, silicon oxide, and polishes the insulating layer by CMP (chemical mechanical polishing) technique. The polishing is carried out until exposure of stopper layers under the insulating layer in the memory area.

[0010] The polishing rate of the insulating layer is, however, not constant but is varied, and the insulating layer in the logic circuit area is polished relatively faster than the insulating layer in the memory area. There is accordingly a possibility that gate electrodes in the logic circuit area are exposed, prior to exposure of the stopper layers in the memory area.

[0011] Exposure of the gate electrodes in the logic circuit area may cause resulting MOS transistors in the logic circuit area to be exposed to an etching gas, which affects the properties of the MOS transistors, in a subsequent process of patterning word gates of memory cells.

SUMMARY OF THE INVENTION

[0012] The object of the present invention is thus to provide a manufacturing method of a semiconductor device, which effectively prevents exposure of gate electrodes in a logic circuit area in an insulating layer polishing process.

[0013] In order to attain at least part of the above and the other related objects, the present invention is directed to a method of manufacturing a semiconductor device, which includes a memory area having a non-volatile memory device and a logic circuit area including a peripheral circuit of the non-volatile memory device. The manufacturing method includes the steps of: (a) providing a semiconductor substrate, which includes a semiconductor layer, a first insulating layer formed on the semiconductor layer, a first conductive layer formed on the first insulating layer, and a stopper layer formed on the first conductive layer; (b) patterning the stopper layer and the first conductive layer in the memory area; (c) forming control gates as side walls on both side faces of the patterned first conductive layer via an oxide nitride oxide (ONO) membrane in the memory area; (d) etching out the stopper layer in the logic circuit area; (e) patterning the first conductive layer in the logic circuit area to form a gate electrode of an insulated gate field effect transistor; (f) forming a second insulating layer in both the memory area and the logic circuit area; and (g) polishing the second insulating layer to expose the stopper layer in the memory area. The step (d) performs over-etching to remove an upper portion of the first conductive layer, simultaneously with removal of the stopper layer.

[0014] The manufacturing method of the invention performs over-etching to remove an upper portion of the first conductive layer in the logic circuit area, simultaneously with etching out the stopper layer. The method subsequently patterns the first conductive layer to form the gate electrode in the logic circuit area. The height of the gate electrode is lowered, because of the removed upper portion of the first conductive layer.

[0015] In the manufacturing method of the invention, the height of the gate electrode formed in the logic circuit area is lowered. In the subsequent process of polishing the second insulating layer, even when the polishing rate of the second insulating layer is not constant but varied and the second insulating layer in the logic circuit area is polished relatively faster than the second insulating layer in the memory area, this arrangement of the invention effectively prevents exposure of the gate electrode in the logic circuit area, prior to exposure of the stopper layer in the memory area.

[0016] In one preferable application of the manufacturing method of the invention, the step (c) includes the sub-steps of: (c-1) forming the ONO membrane in at least the memory area; (c-2) forming a second conductive layer on the ONO membrane; and (c-3) etching the second conductive layer to form the control gates of the second conductive layer via the ONO membrane on both side faces of the patterned first conductive layer in the memory area.

[0017] These sub-steps enable the control gates to be formed as side walls via the ONO membrane on both side face of the patterned first conductive layer.

[0018] In one preferable embodiment of the manufacturing method of the semiconductor device according to the present invention, the step (g) applies CMP technique to polish the second insulating layer.

[0019] This technique is suitable for leveling off the inter-layer insulating layer over the whole surface of the semiconductor substrate.

[0020] The above and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiment with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a plan view schematically illustrating the layout of a memory area in a semiconductor device;

[0022]FIG. 2 is another plan view schematically illustrating the layout of the memory area in the semiconductor device;

[0023]FIG. 3 is a plan view schematically illustrating a main part of the semiconductor memory device;

[0024]FIG. 4 is a sectional view taken on the line A-A in FIG. 2;

[0025]FIG. 5 is a sectional view illustrating one process in a manufacturing method of the semiconductor device shown in FIGS. 1 through 4;

[0026]FIG. 6 is a sectional view illustrating one process in the manufacturing method of the semiconductor device shown in FIGS. 1 through 4;

[0027]FIG. 7 is a plan view showing one process in the manufacturing method of the semiconductor device shown in FIG. 6;

[0028]FIG. 8 is a sectional view illustrating one process in the manufacturing method of the semiconductor device shown in FIGS. 1 through 4;

[0029]FIG. 9 is a sectional view illustrating one process in the manufacturing method of the semiconductor device shown in FIGS. 1 through 4;

[0030]FIG. 10 is a sectional view illustrating one process in the manufacturing method of the semiconductor device shown in FIGS. 1 through 4;

[0031]FIG. 11 is a sectional view illustrating one process in the manufacturing method of the semiconductor device shown in FIGS. 1 through 4;

[0032]FIG. 12 is a sectional view illustrating one process in the manufacturing method of the semiconductor device shown in FIGS. 1 through 4;

[0033]FIG. 13 is a sectional view illustrating one process in the manufacturing method of the semiconductor device shown in FIGS. 1 through 4;

[0034]FIG. 14 is a sectional view illustrating one process in the manufacturing method of the semiconductor device shown in FIGS. 1 through 4;

[0035]FIG. 15 is a sectional view illustrating one process in the manufacturing method of the semiconductor device shown in FIGS. 1 through 4;

[0036]FIG. 16 is a sectional view illustrating one process in the manufacturing method of the semiconductor device shown in FIGS. 1 through 4;

[0037] FIGS. 17(A) and 17(B) show the details of the polishing process by CMP technique;

[0038]FIG. 18 is a sectional view illustrating a stopper layer removing process in a manufacturing method of a semiconductor device in one embodiment of the present invention;

[0039]FIG. 19 is a sectional view illustrating a gate electrode formation process in the manufacturing method of the semiconductor device in the embodiment of the present invention;

[0040]FIG. 20 is a sectional view illustrating an insulating layer formation process in the manufacturing method of the semiconductor device in the embodiment of the present invention;

[0041]FIG. 21 is a sectional view illustrating an insulating layer polishing process by the CMP technique in the manufacturing method of the semiconductor device in the embodiment of the present invention; and

[0042]FIG. 22 is a sectional view illustrating a known MONOS memory cell.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043]FIGS. 1 and 2 are plan views illustrating the layout of a memory area in a semiconductor device manufactured according to a manufacturing method in one embodiment of the present invention. FIG. 3 is a plan view illustrating part of the semiconductor device manufactured according to the manufacturing method in the embodiment of the present invention. FIG. 4 is a sectional view taken on the line A-A in FIG. 3.

[0044] The semiconductor device shown in FIGS. 1 through 4 has a memory area 1000 and a logic circuit area 2000 including peripheral circuits of memories. The memory area 1000 has a memory cell array, in which MONOS non-volatile memory devices (hereafter referred to as ‘memory cells’) 100 are arranged in lattice of multiple rows and multiple columns.

[0045] A. Structure of Device

[0046] The layout of the memory area 1000 is discussed first with reference to FIGS. 1 and 2.

[0047]FIG. 1 shows a first block BI and a second block B2 adjoining to the first block B1 as part of the memory area 1000. FIG. 2 shows the contact structure of the first block B1 with the second block B2.

[0048] An element separating region 300 is formed in a partial area between the first block BI and the second block B2. Multiple word lines 50 (WL) extending in a direction X (in a row direction) and multiple bit lines 60 (BL) extending in a direction Y (in a column direction) are arrayed in each block B1 or B2. Each of the word lines 50 is connected to multiple word gates 14 arranged in the direction X. The bit lines 60 are composed of impurity layers 16 and 18.

[0049] Conductive layers 40 are formed to surround the respective impurity layers 16 and 18 and constitute first and second control gates 20 and 30. The first and the second control gates 20 and 30 respectively extend in the direction Y. The respective one ends of each pair of the first and the second control gates 20 and 30 are connected with each other via the conductive layer 40 extending in the direction X. The respective other ends of each pair of the first and the second control gates 20 and 30 are linked with one common contact element 200. The first and the second control gates 20 and 30 accordingly have general functions as the control gate of the memory cell and wiring functions of connecting the paired control gates arranged in the direction Y.

[0050] Each memory cell 100 has one word gate 14, the first and the second control gates 20 and 30 arranged on both sides of the word gate 14, and the impurity layers 16 and 18 that are formed in the semiconductor substrate and located outside these control gates 20 and 30. The impurity layers 16 and 18 are shared by the adjoining memory cells 100.

[0051] The two impurity layers 16 adjoining to each other in the direction Y, that is, the impurity layer 16 formed in the block BI and the impurity layer 16 formed in the adjoining block B2, are electrically connected with each other via a contact impurity layer 400 formed in the semiconductor substrate. The contact impurity layer 400 is located opposite to the common contact element 200 of the control gates across the impurity layer 16.

[0052] A contact 350 is formed on each contact impurity layer 400. The bit lines 60 of the impurity layers 16 are electrically linked with an upper wiring layer via the contacts 350.

[0053] Similarly, the two impurity layers 18 adjoining to each other in the direction Y are electrically connected with each other via the contact impurity layer 400 on the side without the common contact element 200 (see FIG. 2).

[0054] As shown in FIG. 1, the planar layout of the multiple common contact elements 200 in each block has a zigzag pattern, where the common contact elements 200 are arranged alternately on different sides of the impurity layers 16 and 18. Similarly, as shown in FIG. 2, the planar layout of the multiple contact impurity layers 400 in each block has a zigzag pattern, where the contact impurity layers 400 are arranged alternately on different sides of the impurity layers 16 and 18.

[0055] The planar structure and the sectional structure of the semiconductor device are discussed with reference to FIGS. 3 and 4. The logic circuit area 2000 including peripheral circuits of memories is formed adjacent to the memory area 1000. The memory area 1000 is electrically separated from the logic circuit area 2000 by means of the element separating region 300. The memory area 1000 includes at least the multiple memory cells 100. The logic circuit area 2000 includes at least insulated gate field effect transistors (hereafter referred to as ‘MOS transistors’) 500 constructing logic circuits.

[0056] The description first regards the memory area 1000.

[0057] As shown in FIG. 4, each memory cell 100 includes the word gate 14 that is formed on a semiconductor substrate 10 via a first gate insulating layer 12, the impurity layers 16 and 18 that are formed in the semiconductor substrate 10 to constitute either a source area or a drain area, and the first and the second control gates 20 and 30 that are formed as side walls along both sides of the word gate 14. Silicide layers 92 are arranged on the top of the impurity layers 16 and 18.

[0058] The first control gate 20 is arranged on the semiconductor substrate 10 via a second gate insulating layer 22 and on one side face of the word gate 14 via a side insulating layer 24. Similarly the second control gate 30 is arranged on the semiconductor substrate 10 via the second gate insulating layer 22 and on the other side face of the word gate 14 via the side insulating layer 24.

[0059] The second gate insulating layer 22 and the side insulating layer 24 are ONO membranes. More specifically, the second gate insulating layer 22 and the side insulating layer 24 are multi-layered membranes including a silicon oxide bottom layer (first silicon oxide layer (O)), a silicon nitride layer (N), and a silicon oxide top layer (second silicon oxide layer (O)).

[0060] The first silicon oxide layer of the second gate insulating layer 22 makes a potential barrier between a channel area and a charge accumulation region.

[0061] The silicon nitride layer of the second gate insulating layer 22 functions as a charge accumulation region for trapping carriers (for example, electrons).

[0062] The second silicon oxide layer of the second gate insulating layer 22 makes a potential barrier between the control gate and the charge accumulation region.

[0063] The side insulating layer 24 electrically separates the word gate 14 from the control gates 20 and 30. In order to prevent a short circuit between the word gate 14 and the first and the second control gates 20 and 30, the upper end of the side insulating layer 24 is located above the upper ends of the control gates 20 and 30 relative to the semiconductor substrate 10.

[0064] The side insulating layer 24 and the second gate insulating layer 22 are produced by the same film forming process and have the identical layer structure.

[0065] An embedded insulating layer 70 is disposed between the first control gate 20 and the second control gate 30 of the adjoining memory cells 100. The embedded insulating layer 70 covers over at least the control gates 20 and 30 to prevent exposure thereof. In the concrete structure, the upper face of the embedded insulating layer 70 is located above the upper end of the side insulating layer 24 relative to the semiconductor substrate 10. Such arrangement of the embedded insulating layer 70 ensures the electrical separation of the first and the second control gates 20 and 30 from the word gates 14 and the word lines 50.

[0066] A conductive layer is formed on the common contact element 200 to apply a predetermined potential to the control gates 20 and 30. The common contact element 200 includes a first contact insulating layer 212, a second contact insulating layer 210, a first contact conductive layer 214, a second contact conductive layer 232, a third contact insulating layer 252, and a third contact conductive layer 260.

[0067] The first contact insulating layer 212 is produced by the same manufacturing process as that of the first gate insulating layer 12.

[0068] The second contact insulating layer 212 is produced by the same manufacturing process as that of the second gate insulating layer 22 and the side insulating layer 24. The second contact insulating layer 210 is a multi-layered ONO membrane including a first silicon oxide layer, a silicon nitride layer, and a second silicon oxide layer.

[0069] The first contact conductive layer 214 is produced by the same manufacturing process as that of the word gate 14. The first contact conductive layer 214 is formed outside the second contact insulating layer 210.

[0070] The second contact conductive layer 232 is formed inside the second contact insulating layer 210. The second contact conductive layer 232 is produced by the same manufacturing process as that of the first and the second control gates 20 and 30 to be integrated with these control gates 20 and 30. Namely the second contact conductive layer 232 and the control gates 20 and 30 are made of an identical material.

[0071] The third contact insulating layer 252 is formed inside the second contact conductive layer 232. The third contact insulating layer 252 is produced by the same manufacturing process as that of side wall insulating layers 152.

[0072] The third contact conductive layer 260 is produced by the same manufacturing process as that of the word line 50 and is linked with the first contact conductive layer 214 and the second contact conductive layer 232.

[0073] The MOS transistors 500 are created in the logic circuit area 2000. Each MOS transistor 500 includes a gate electrode 142 that is created on the semiconductor substrate 10 via a third gate insulating film 122, impurity layers 162 and 182 that are formed in the semiconductor substrate 10 to constitute either a source area or a drain area, and side wall insulating layers 152 that are formed along both sides of the gate electrode 142. Silicide layers 192 are arranged on the top of the impurity layers 162 and 182, and a silicide layer 194 is arranged on the top of the gate electrode 142.

[0074] In the logic circuit area 2000, the MOS transistors 500 are covered with an insulating layer 270. This insulating layer 270 is produced by the same manufacturing process as that of the embedded insulating layer 70.

[0075] As shown in FIGS. 3 and 4, a boundary element 140 c, which is composed of the same material as that of the word gate 14 and the gate electrode 142, is arranged in a boundary region between the memory area 1000 and the logic circuit area 2000. The boundary element 140 c is produced by the same film forming process as that of the word gate 14 and the gate electrode 142. At least part of the boundary element 140 c is formed above the element separating region 300.

[0076] A side wall conductive layer 20 a, which is composed of the same material as that of the control gates 20 and 30, is arranged on one side face of the boundary element 140 c (on the side of the memory area 1000). The side wall conductive layer 20 a extends in the direction Y and is electrically connected with the adjoining control gate 30 via the common contact element 200. The side wall conductive layer 20 a is not used as the control gate of the memory cell. The electrical connection of the side wall conductive layer 20 a with the adjoining control gate 30 causes the electric properties of the control gate 30 adjacent to the side wall conductive layer 20 a to be substantially equal to the electric properties of the other control gates.

[0077] A side wall insulating layer 152, which is produced by the same manufacturing process as that of the side wall insulating layers 152 of the MOS transistor 500, is arranged on the other side face of the boundary element 140 c (on the side of the logic circuit area 2000).

[0078] An inter-layer insulating layer 72 is formed on the semiconductor substrate 10 with the memory cells 100 and the MOS transistors 500. The inter-layer insulating layer 72 has contact holes, which run to, for example, the third contact conductive layer 260 of the common contact element 200. Each contact hole is filled with a conductive layer 82 of, for example, a tungsten plug or a copper plug, which is connected to a wiring layer 80 located above the inter-layer insulating layer 72.

[0079] B. Basic Manufacturing Method of Semiconductor Device

[0080] Prior to description of a manufacturing method of a semiconductor device in one embodiment of the present invention, a basic manufacturing method is discussed with reference to FIGS. 5 through 16. The respective sectional views of FIGS. 5 through 16 correspond to the part taken on the line A-A in FIG. 3. In the drawings of FIGS. 5 through 16, like elements to those shown in FIGS. 1 through 4 are expressed by like numerals and are not specifically described here.

[0081] (1) Referring to FIG. 5, the method first forms the element separating regions 300 on the surface of the semiconductor substrate 10 by the technique of trench isolation. The method then forms the contact impurity layers 400 (see FIG. 1) in the semiconductor substrate 10 by the technique of ion implantation.

[0082] The method subsequently forms an insulating layer 120, which constructs the gate insulating layers, on the surface of the semiconductor substrate 10, and makes a gate layer 140, which constructs the word gates 14 and the gate electrodes 142, deposit on the insulating layer 120. The gate layer 140 is made of doped polysilicon. A stopper layer S100, which works as an indication of the end of polishing in a later CMP (Chemical Mechanical Polishing) process is further formed on the gate layer 140. The stopper layer S100 is composed of the silicon nitride layer.

[0083] The insulating layer 120, the gate layer 140, and the stopper layer S100 respectively correspond to the first insulating layer, the first conductive layer, and the stopper layer of the present invention.

[0084] (2) Referring to FIG. 6, a patterned gate layer 140 a is formed in the memory area 1000. One concrete procedure for formation of the patterned gate layer 140 a forms a resist layer (not shown) on the stopper layer S100 (see FIG. 5) to cover over the whole logic circuit area 2000 and to be extended to part of the memory area 1000. The procedure then patterns the stopper layer S100 with the resist layer as the mask, and etches the gate layer 140 with the patterned stopper layer as the mask. This results in patterning the gate layer 140 to give the patterned gate layer 140 a shown in FIG. 6. In this process, the gate layer 140 in the logic circuit area 2000 is not patterned. As a matter of convenience, hereafter the gate layer 140 in the logic circuit area 2000 is called the gate layer 140 b.

[0085]FIG. 7 is a plan view showing the state of the memory area 1000 after patterning. The patterning makes openings 160 and 180 in the multi-layered body of the gate layer 140 and the stopper layer S100 in the memory area 1000. The openings 160 and 180 substantially correspond to the regions in which the impurity layers 16 and 18 are formed by a later ion implantation process. The side insulating layers and the control gates are formed afterwards along the side faces of the openings 160 and 180.

[0086] (3) Referring to FIG. 8, an ONO membrane 220 is formed over the whole face of the semiconductor substrate 10. The ONO membrane 220 is obtained by successive deposition of a first silicon oxide layer (O), a silicon nitride layer (N), and a second silicon oxide layer (O). The first silicon oxide layer is formed, for example, by thermal oxidation technique or CVD technique. The silicon nitride layer is formed, for example, by CVD technique. The second silicon oxide layer is formed, for example, by CVD technique or more specifically by high temperature oxidation (HTO) technique. The preferable procedure carries out annealing treatment after formation of these layers to densify the respective layers.

[0087] A later patterning process of the ONO membrane 220 makes the second gate insulating layer 22, the side insulating layer 24, and the second contact insulating layer 210 (see FIG. 4).

[0088] (4) Referring to FIG. 9, a doped polysilicon layer 230 is made to deposit over the whole surface of the ONO membrane 220. A later etching process of the doped polysilicon layer 230 gives the conductive layer 40 (see FIG. 1) of the control gates 20 and 30 and the second conductive layer 232 (see FIG. 3) of the common contact element 200.

[0089] A resist layer R100 is then formed in the region for the common contact element 200.

[0090] (5) Referring to FIG. 10, anisotropic etching of the whole doped polysilicon layer 230 (see FIG. 9) with the resist layer R100 as the mask gives the first and the second control gates 20 and 30 and the second contact conductive layer 232.

[0091] This etching process makes the control gates 20 and 30 as the side walls along the side faces of the openings 160 and 180 (see FIG. 7) in the memory area 1000. Simultaneously, the second contact conductive layers 232 are formed in the masked parts with the resist layer R100 (see FIG. 9). The doped polysilicon layer 230 depositing in the logic circuit area 2000 is completely removed. In the boundary region, however, the doped polysilicon layer 230 remains as a side wall on the side face of one end of the gate layer 140 b (on the side of the memory area 1000). The resist layer R100 is then removed.

[0092] The ONO membrane 220, the control gates 20 and 30, and the doped polysilicon layer 230 respectively correspond to the ONO membrane, the control gate, and the second conductive layer of the present invention.

[0093] (6) Referring to FIG. 11, a resist layer R200 is then formed to cover over the whole memory area 1000 and to be extended to part of the logic circuit area 2000. The ONO membrane 220 and the stopper layer S100 in the logic circuit area 2000 are removed with the resist layer R200 as the mask. This etching process removes all the stopper layer S100 in the logic circuit area 2000 except the boundary region.

[0094] The part of the gate layer 140 b located in the boundary region between the memory area 1000 and the logic circuit area 2000 and covered with both the resist layer used in the etching process (2) (see FIG. 6) and the resist layer R200 used in the etching process (6) forms the boundary element 140 c (see FIG. 4) in a later process. A stopper layer S100 a remaining through this patterning process has a greater width than the width of the remaining stopper layers S100 in the memory area 1000. The resist layer R200 is removed subsequently.

[0095] (7) Referring to FIG. 12, a resist layer R300 is formed for creation of the gate electrodes 142. The resist layer R300 is patterned to cover over the whole memory area 1000 and a predetermined part in the logic circuit area 2000. Etching of the gate layer 140 b (see FIG. 11) with the resist layer R300 as the mask gives the gate electrodes 142 in the logic circuit area 2000. This etching process also gives the boundary element 140 c in the boundary region in a self aligning manner with the resist layer R300 and the stopper layer S100 a as the mask.

[0096] The resist layer R300 is then removed. Subsequent doping of an N-type impurity creates extension layers 161 and 181 of the source areas and the drain areas in the logic circuit area 2000.

[0097] (8) Referring to FIG. 13, an insulating layer 250 of silicon oxide or silicon oxide nitride is formed over the memory area 1000 and the logic circuit area 2000.

[0098] (9) Referring to FIG. 14, anisotropic etching of the whole insulating layer 250 (see FIG. 13) gives the side wall insulating layers 152 on both sides of each gate electrode 142 in the logic circuit area 2000. Simultaneously, the anisotropic etching gives the side wall insulating layer 152 on one side face of the boundary element 140 c facing the logic circuit area 2000. This etching process also makes insulating layers 152 a remain on the control gates 20 and 30, and forms the third contact insulating layer 252 covering over the second contact conductive layer 232. The etching process removes the insulating layers depositing on specified regions for formation of silicide layers in a later process and on the gate electrodes 142 in the logic circuit area 2000 to expose the semiconductor substrate 10. The specific regions include, for example, regions for formation of the impurity layers 16 and 18 in the memory area 1000 and regions for formation of the impurity layers 162 and 182 in the logic circuit area 2000 in a later ion implantation process.

[0099] Subsequent implantation of an N-type impurity ion forms the impurity layers 16 and 18, each of which constitutes either a source area or a drain area in the memory area 1000, and the impurity layers 162 and 182, each of which constitutes either a source area or a drain area in the logic circuit area 2000, in the semiconductor substrate 10.

[0100] A subsequent process makes a metal for formation of a suicide deposit on the whole surface. Typical examples of the metal for formation of the silicide are titanium and cobalt. The metal depositing on the impurity layers 16, 18, 162, and 182 and the gate electrodes 142 is subjected to a silicidation reaction. This forms the silicide layers 92 on the top of the impurity layers 16 and 18, the silicide layers 192 on the top of the impurity layers 162 and 182, and the silicide layer 194 on the top of the gate electrodes 142. This silicidation process silicidates the gate electrodes and either the source areas or the drain areas of the MOS transistors 500 (see FIG. 4) in a self aligning manner in the logic circuit area 2000. Simultaneously, the silicidation process silicidates the surface of either the source areas or the drain areas of the memory cells 100 (see FIG. 4) in a self aligning manner in the memory area 1000.

[0101] The insulating layer 270 of silicon oxide or silicon oxide nitride is formed over the whole surface of the memory area 1000 and the logic circuit area 2000. The insulating layer 270 is formed to cover over the stopper layers S100 and S100 a.

[0102] (10) Referring to FIG. 15, the insulating layer 270 is polished by the CMP technique to exposure of the stopper layers S100 and S100 a and is leveled off. The polishing makes the insulating layer 270 remain between the two side insulating layers 24 facing each other across the control gates 20 and 30 to define the embedded insulating layer 70.

[0103] The upper ends of the side insulating layers 24 formed on the side faces of the gate layer 140 a and the stopper layer S100 are located above the upper ends of the first and the second control gates 20 and 30 relative to the semiconductor substrate 10. It is preferable that the MOS transistors 500 are completely covered with the insulating layer 270 in the logic circuit area 2000.

[0104] On completion of this polishing process, the stopper layers S100 and S100 a are accordingly present on the gate layer 140 a, which constructs the word gates 14, and the boundary element 140 c, respectively. No stopper layer is present on the gate electrodes 142, but the gate electrodes 142 are covered with the insulating layer 270.

[0105] (11) The stopper layers S100 and S100 a (see FIG. 15) are removed with hot phosphoric acid. This results in exposure of at least the upper faces of the gate layer 140 a and the boundary element 140 c. A doped polysilicon layer is then made to deposit on the whole surface.

[0106] Referring to FIG. 16, a patterned resist layer R400 is subsequently formed on the depositing doped polysilicon layer. Patterning of the doped polysilicon layer with the resist layer R400 as the mask gives the word lines 50 and the third contact conductive layer 260.

[0107] The gate layer 140 a (see FIG. 15) is etched with the resist layer R400 as the mask. The etching removes part of the gate layer 140 a where the word lines 50 are not formed thereon. This gives the word gates 14 arranged in an array. The removed part of the gate layer 140 a corresponds to the region of a P-type impurity layer (element separating impurity layer) 15 created in a later process (see FIG. 3).

[0108] The conductive layer 40, which constructs the first and the second control gates 20 and 30, is covered with the embedded insulating layer 70 and is thus not etched but remains by this etching process. The MOS transistors 500 in the logic circuit area 2000 are not affected by this etching process, as long as the MOS transistors 500 are completely covered with the insulating layer 270.

[0109] The whole semiconductor substrate 10 is then doped with a P-type impurity. The P-type impurity layer (element separating impurity layer) 15 (see FIG. 3) is accordingly formed between each pair of the word gates 14 adjoining to each other in the direction Y. The P-type impurity layer 15 ensures separation between the adjoining memory cells 100.

[0110] (12) The process subsequently forms a first inter-layer insulating layer, makes contact holes by any known method, and creates a conductive layer in each contact hole and a first wiring layer. For example, as shown in FIG. 4, the process forms the inter-layer insulating layer 72, makes contact holes in the inter-layer insulating layer 72, and creates the conductive layer 82 and the wiring layer 80 connecting with each contact element 200. This process simultaneously creates contact elements and a wiring layer in the logic circuit area 2000.

[0111] The series of processes discussed above manufactures the semiconductor device shown in FIGS. 1 through 4.

[0112] C. Details of Polishing Process of Insulating Layer by CMP Technique

[0113] FIGS. 17(A) and 17(B) show the details of the polishing process by the CMP technique (see FIG. 15) discussed above in the process (10). FIG. 17 schematically illustrates the sectional area of the main part of the memory area and the logic circuit area in the semiconductor device.

[0114] As discussed above in the process (9), after the silicidation process, the insulating layer 270 is formed over the whole surface of the memory area 1000 and the logic circuit area 2000 (see FIG. 14). In the actual state, as shown in FIG. 17(A), there are irregularities on the top surface of the insulating layer 270, which correspond to the gate layers 140 a in the memory area 1000 and the gate electrodes 142 in the logic circuit area 2000 under the insulating layer 270. The gate layers 140 a are formed at a relatively high density in the memory area 1000, while the gate electrodes 142 are formed at a relatively low density in the logic circuit area 2000. The density of the irregularities on the top surface of the insulating layer 270 is thus relatively high in the memory area 1000 and is relatively low in the logic circuit area 2000. Especially the region of the memory area 1000 with the array of multiple memory cells 100 has a higher density of irregularities, compared with the logic circuit area 2000.

[0115] After formation of the insulating layer 270, the insulating layer 270 is polished by the CMP technique to exposure of the stopper layers S100 and S100 a, as discussed above in the process (10). There may be a variation in polishing rate of the insulating layer 270, due to the varying density of the irregularities present on the top surface of the insulating layer 270. More specifically, the insulating layer 270 in the logic circuit area 2000 having a relatively low density of the irregularities is polished relatively faster than the insulating layer 270 in the memory area 1000 having a relatively high density of the irregularities. This causes exposure of the gate electrodes 142 in the logic circuit area 2000, prior to exposure of the stopper layers S100 a in the memory area 1000 as shown in FIG. 17(B).

[0116] Exposure of the gate electrodes 142 causes the MOS transistors 500 in the logic circuit area 2000 to be exposed to the etching gas, which may affect the properties of the MOS transistors 500 in the process (11) discussed above (see FIG. 16), for example, in the process of patterning the word gates 14 of the memory cells 100 in the memory area 1000.

[0117] In the polishing process (10) by the CMP technique discussed above, the gate electrodes 142 in the logic circuit area 2000 may be exposed, prior to exposure of the stopper layers S100 a in the memory area 1000. This may cause the MOS transistors 500 in the logic circuit area 2000 to be exposed to the etching gas and change their properties in the subsequent process.

[0118] D. Manufacturing Method of Embodiment

[0119] A manufacturing method of a semiconductor device in one embodiment of the present invention changes the process of removing the stopper layer from the process (6) discussed above and shown in FIG. 11 to a process shown in FIG. 18, and then carries out the process (10) of polishing the insulating layer 270 by the CMP technique discussed above.

[0120]FIG. 18 is a sectional view illustrating a stopper layer removing process in the manufacturing method of the semiconductor device in the embodiment of the present invention. The cross section of a main part of the memory area and the logic circuit area in the semiconductor device is schematically shown in FIG. 18.

[0121] Referring to FIG. 18, after formation of the resist layer R200, the process performs over-etching to remove the upper portion of the gate layer 140 b located below the stopper layer S100, simultaneously with removal of the ONO membrane 220 and the stopper layer S100 in the logic circuit area 2000 with the resist layer R200 as the mask. This etching process removes the whole stopper layer S100 and the upper portion of the gate layer 140 b in the logic circuit area 2000 except the boundary region.

[0122]FIG. 19 is a sectional view illustrating a gate electrode formation process in the manufacturing method of the semiconductor device in the embodiment of the present invention. FIG. 20 is a sectional view illustrating an insulating layer formation process. The process of FIG. 19 corresponds to the process (7) discussed above and shown in FIG. 12. The process of FIG. 20 corresponds to the process (9) discussed above and shown in FIG. 14. The cross section of the main part of the memory area and the logic circuit area in the semiconductor device is schematically shown in FIGS. 19 and 20.

[0123] As discussed above, the stopper layer removal process removes the upper portion of the gate layer 140 b in the logic circuit area 2000 by the over-etching technique. The subsequent gate electrode formation process etches the gate layer 140 b with the resist layer R300 as the mask and creates the gate electrodes 142 in the logic circuit area 2000, as discussed above in the process (7). The height of the gate electrodes 142 created in the process of FIG. 19 is lower than the height of the gate electrodes 142 created in the process of FIG. 12.

[0124] The subsequent insulating layer formation process forms the insulating layer 270 over the whole surface of the memory area 1000 and the logic circuit area 2000, as discussed above in the process (9). The insulating layer 270 in the logic circuit area 2000 has the top surface as shown in FIG. 20. The density of creation of the gate electrodes 142 is unchanged in the logic circuit area 2000, while the height of the gate electrodes 142 is lowered in the logic circuit area 2000 by over-etching. The density of the irregularities on the top surface of the insulating layer 270 in the logic circuit area 2000 is accordingly kept lower than that in the memory area 1000. The height of the irregularities on the top surface of the insulating layer 270 in the logic circuit area 2000 is, however, slightly lowered due to the lower height of the gate electrode 142, compared with the case of FIG. 17(A).

[0125] The gate electrode 142 and the insulating layer 270 respectively correspond to the gate electrode and the second insulating layer of the present invention.

[0126] After the above series of operations, the process of polishing the insulating layer by the CMP technique is carried out as discussed above in the process (10).

[0127]FIG. 21 is a sectional view illustrating an insulating layer polishing process by the CMP technique in the manufacturing method of the semiconductor device in the embodiment of the present invention. The cross section of the main part of the memory area and the logic circuit area in the semiconductor device is schematically shown in FIG. 21.

[0128] As described above, polishing the insulating layer 270 by the CMP technique keeps the lower density of the irregularities on the top surface of the insulating layer 270 in the logic circuit area 2000, compared with that in the memory area 1000. The insulating layer 270 in the logic circuit area 2000 is polished relatively faster than the insulating layer 270 in the memory area 1000. The height of the gate electrodes 142 in the logic circuit area 2000 is lowered by over-etching, as discussed above. When the insulating layer 270 is polished to exposure of the stopper layers S100 a in the memory area 1000, there is no possibility that the gate electrodes 142 in the logic circuit area 2000 are exposed prior to exposure of the stopper layers S100 a.

[0129] As discussed above, the manufacturing method of the semiconductor device in the embodiment effectively prevents exposure of the gate electrodes 142 in the logic circuit area 2000 prior to exposure of the stopper layers S100 a in the memory area 1000 in the insulating layer polishing process by the CMP technique.

[0130] At the stage of completion of the polishing process by the CMP technique, the MOS transistors 500 in the logic circuit area 2000 are completely covered with the insulating layer 270. The insulating layer 270 has a certain thickness ‘e’ above the gate electrode 142.

[0131] The subsequent word gate formation process etches out a desired part of the gate layer 140 a in the memory area 1000 to create an array of the word gates 14 as discussed previously in the process (11). The arrangement of the embodiment effectively prevents the gate electrodes 142 in the logic circuit area 2000 from being affected by the etching.

[0132] In the stopper layer removal process of FIG. 18, the removed thickness ‘d’ of the upper portion of the gate layer 140 b in the logic circuit area 2000 by over-etching is appropriately set by taking into account the polishing rate in the insulating layer polishing process by the CMP technique and the properties of the MOS transistors 500.

[0133] The lower limit of the removed thickness ‘d’ of the gate layer 140 b is set to ensure prevention of exposure of the gate electrodes 142 in the logic circuit area 2000 prior to exposure of the stopper layers 100 a in the memory area 1000 in the insulating layer polishing process by the CMP technique. The upper limit of the removed thickness ‘d’ is set to leave a sufficient height of the gate electrodes 142 in the logic circuit area 2000 for the required functions of the resulting MOS transistors 500.

[0134] The above embodiment and its application are to be considered in all aspects as illustrative and not restrictive. There may be many modifications, changes, and alterations without departing from the scope or spirit of the main characteristics of the present invention.

[0135] In the embodiment discussed above, the processes (2) through (5) form the gate layers 140 a and the control gates 20 and 30 in the memory area 1000, and the subsequent processes (6) through (9) form the gate electrodes 142 and the side wall insulating layers 152 in the logic circuit area 2000. The technique of the present invention is, however, not limited to this order of operations. The process may inversely form the gate electrodes 142 and the side wall insulating layers 152 in the logic circuit area 2000, prior to formation of the gate layers 140 a and the control gates 20 and 30 in the memory area 1000.

[0136] The bulk semiconductor substrate is applied for the semiconductor layer of the embodiment. An SOI semiconductor substrate may alternatively be applied for the semiconductor layer.

[0137] The scope and spirit of the present invention are indicated by the appended claims, rather than by the foregoing description. 

What is claimed is:
 1. A method of manufacturing a semiconductor device, which comprises a memory area having a non-volatile memory device and a logic circuit area including a peripheral circuit of the non-volatile memory device, the manufacturing method comprising the steps of: (a) providing a semiconductor substrate, which includes a semiconductor layer, a first insulating layer formed on the semiconductor layer, a first conductive layer formed on the first insulating layer, and a stopper layer formed on the first conductive layer; (b) patterning the stopper layer and the first conductive layer in the memory area; (c) forming control gates as side walls on both side faces of the patterned first conductive layer via an oxide nitride oxide (ONO) membrane in the memory area; (d) etching out the stopper layer in the logic circuit area; (e) patterning the first conductive layer in the logic circuit area to form a gate electrode of an insulated gate field effect transistor; (f) forming a second insulating layer in both the memory area and the logic circuit area; and (g) polishing the second insulating layer to expose the stopper layer in the memory area, wherein the step (d) performs over-etching to remove an upper portion of the first conductive layer, simultaneously with removal of the stopper layer.
 2. A manufacturing method in accordance with claim 1, wherein the step (c) comprises the sub-steps of: (c-1) forming the ONO membrane in at least the memory area; (c-2) forming a second conductive layer on the ONO membrane; and (c-3) etching the second conductive layer to form the control gates of the second conductive layer via the ONO membrane on both side faces of the patterned first conductive layer in the memory area.
 3. A manufacturing method in accordance with claim 1, wherein the step (g) applies chemical mechanical polishing (CMP) technique to polish the second insulating layer.
 4. A manufacturing method in accordance with claim 2, wherein the step (g) applies chemical mechanical polishing (CMP) technique to polish the second insulating layer. 